This invention relates generally to turbomachines. More specifically, the invention is directed to methods and apparatus for impeding the flow of gas (e.g., hot gas) through selected regions of stator-rotor assemblies in turbomachines, such as turbine engines.
In operation of at least some known turbine engines, intake air is channeled towards a compressor where it is compressed to higher pressures and temperatures prior to being discharged towards a combustor section. The compressed air is channeled to a fuel nozzle assembly, mixed with fuel, and burned within each combustor to generate combustion gases that are channeled downstream through a rotor/stator cavity of a turbine section. The combustion gases impinge upon rotor blades positioned within the turbine to convert thermal energy into mechanical rotational energy that is used to drive a rotor assembly. The turbine section drives the compressor section and/or a load, via separate drive shafts, and discharges exhaust gases to the ambient atmosphere.
At least some known gas turbine engines define a wheelspace radially inward of the rotor/stator cavity that includes components fabricated from materials having a temperature resistance that is lower than temperatures present in the rotor/stator cavity. Furthermore, at least some known rotor blades include a shank, and a connecting structure coupled to the shank, such as a dovetail, used to couple a rotor blade to a rotor wheel. An airfoil is also coupled to the shank such that the airfoil is exposed to the hot combustion gases.
In at least some known rotor blade constructions, structures commonly referred to as “angel wings,” extend axially fore and/or aft from the shank. In at least some known gas turbine engines, at least one angel wing extends from an upstream-facing shank wall and/or a downstream-facing shank wall of a rotor blade and under-hangs a platform portion of an adjacent stator to define a substantially constant gap therebetween. The stator platform and rotor angel wing combine to at least partially prevent channeling of hot combustion gases into a buffer cavity defined radially inward of the angel wing. Reducing the amount of hot combustion gas channeled into the wheelspace is desirable to prevent reducing the operational lifetime of wheelspace components due to exposure to the hot combustion gases.
In at least some known gas turbine engines, cooling air is channeled under pressure into the inner wheelspace to facilitate reducing an amount of hot combustion gas channeled into the inner wheelspace. However, the channeling of cooling air into the inner wheelspace may have the effect of reducing engine efficiency. Furthermore, the size of the gap defined between the stator platform and the angel wing must accommodate transient events in the engine due to rotation of the rotor and expansion of certain turbine components due to heat. The gap is large enough to provide a path which can allow hot combustion gases into the wheelspace and, therefore, requires an amount of the cooling air that may negatively affect engine efficiency.